The present invention generally relates to totally enclosed motors and in particular to a system and method of facilitating cooling of internal components of a totally enclosed motor.
Electric motors generate heat during operation as a result of both electrical and mechanical losses, and an electric motor typically must be cooled in order to ensure the desired and efficient operation of the motor. An excessively high motor temperature may result in motor bearing failure or damage to the stator winding insulation. Electric motors generally have an enclosure, or housing, including a frame and end brackets. Some of the most common enclosures include open enclosures and totally enclosed enclosures. With an open enclosure, ambient air circulates within the enclosure, and heat is removed by convection between the air and heat generating motor components within the enclosure. The heated air is exhausted out from the enclosure.
Totally enclosed type enclosures typically are used in applications in which airborne contaminants (e.g., dirt, oil, or mist), must be prevented from entering within the enclosure. There is no communication of air through the enclosure and thus no possibility of bringing cooling air from outside the enclosure into the interior. Both convection and conduction type cooling occurs within the enclosure, and some form of convection cooling occurs at the external surfaces of the enclosure. For example, a fan mounted to the motor shaft provides forced convection cooling. The fan forces air over the frame and end brackets. However this system can be unsatisfactory to cool the bearings. The heating of the bearing is primarily the result of the air inside the motor that is elevated in temperature by the heat generated by the rotor and stator windings and friction losses in the bearing.
The prior art has attempted to cool bearings in totally enclosed motors by cooling an outside surface thermally coupled to the bearing by an external shaft fan. The arrangement was unsatisfactory since the external fan was noisy, reduced motor efficiency and was often covered by a customer coupling guard. The prior art has attempted to circulate the air internal the motor. This was also unsatisfactory since there was little transfer of heat from the inside of the motor to an outside ambient. Circulation of the internal air, which is elevated in temperature, is totally inadequate to cool the bearing. Other methods attempted by the prior art include enlarging the case for more cooling surface area, rating the motors for a lower power rating for a given fan RPM.
Therefore, there is an unmet need in the art to provide improvements in cooling of the bearings of totally enclosed motors for maintaining the reliability of the motor during normal operations.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention provides for a system and method that facilitates cooling of the bearings of a totally enclosed motor. The totally enclosed motor of the present invention includes a cylindrical frame coupled to a first circular end bracket and a second circular end bracket. The first end bracket is located at a drive end of the motor while the second end bracket is located opposite the drive end of the motor. Within the frame is an electrical core for providing energy to the motor. The electrical core consists of a stator, a rotor, and any additional circuitry and wiring required to operate the motor. The rotor is mounted on a rotor shaft. The rotor shaft assembly is supported by bearing assemblies located in both the first end bracket and second end bracket. The stator and rotor produces heat while providing energy to the motor. The present invention provides for a system and method of providing cooling air in addition to isolating at least one of the bearings to improve bearing life.
According to one aspect of the present invention, an improved cooling system for a totally enclosed motor includes a first thermal barrier coupled to the first end bracket and operable to insulate the bearing located at the drive end of the motor. Either an external fan located opposite the drive end of the motor or an externally mounted blower may be employed to provide cooling air to the motor. Moreover, a second thermal barrier operable to insulate bearings located opposite the drive end of the motor may be coupled to the second end bracket.
According to another aspect of the present invention, an improved cooling system for a totally enclosed motor includes an air deflector coupled to the drive end of the motor. The air deflector is operable to capture the cooling air provided by the external fan or the blower and direct it as high velocity air over the first end bracket, thereby keeping the bearing supported within the first end bracket cool. Alternatively an external fan may be coupled to the drive end of the motor to provide cooling air to the first end bracket.